High efficiency blood pump

ABSTRACT

Blood pumps discussed herein may be suitable for use as a ventricular assist device (VAD) or the like. The blood pumps cause minimal blood damage, are energy efficient, and can be powered by implanted batteries for extended periods of time. Further, these pumps are also beneficial because they may improve the quality of life of a patient with a VAD by reducing restrictions on the patient&#39;s lifestyle. The blood pumps can provide radial and axial stability to a rotating impeller that is driven by a separate rotor. Both radial and axial stability can be provided, at least in part, by one or more permanent magnetic couplings between the rotor and the impeller and/or one or more permanent magnetic bearings between the pump housing and the impeller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/532,212, entitled “HIGH EFFICIENCY BLOOD PUMP,” filed Jul. 13, 2017,and U.S. Provisional Application No. 62/571,708, entitled “HIGHEFFICIENCY BLOOD PUMP,” filed Oct. 12, 2017, the entirety of each ofwhich is incorporated herein by reference.

TECHNICAL FIELD

The present description relates in general to blood pumps, and moreparticularly to, for example, without limitation, implantable rotaryblood pumps.

BACKGROUND OF THE DISCLOSURE

Implantable blood pumps can be utilized for total artificial heartreplacement or ventricular assistance. Implantable blood pumps may beutilized for temporary or long term ventricular assistance or topermanently replace a patient's damaged heart.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top plan view of an illustrative embodiment of a pump.

FIG. 2 shows a cross-sectional side view of the pump taken along sectionlines A-A of FIG. 1.

FIG. 3 shows a cross-sectional top view of the pump taken along sectionlines B-B of FIG. 2.

FIG. 4 shows an enlarged cross-sectional side view of the pump ofsection C of FIG. 2.

FIG. 5A shows a cross-sectional view of an impeller.

FIG. 5B shows a cross-sectional view of an illustrative embodiment of apump housing.

FIG. 5C shows a cross-sectional view of an illustrative embodiment of amotor and motor housing.

FIG. 6A shows a top perspective view of an illustrative embodiment of animpeller.

FIG. 6B shows a bottom perspective view of the impeller of FIG. 6A.

FIG. 6C shows a bottom plan view of the impeller of FIG. 6A.

FIG. 7A shows top plan view of an illustrative embodiment of a motor andcarrier.

FIG. 7B shows a perspective view of the motor and carrier of FIG. 7A.

FIG. 8 shows a top view of an illustrative embodiment of a pump.

FIG. 9 shows a cross-sectional side view of the pump taken along sectionlines A-A of FIG. 8.

FIG. 10 shows a cross-sectional top view of the pump taken along sectionlines B-B of FIG. 9.

FIG. 11 shows an enlarged cross-sectional side view of the pump ofsection C of FIG. 9.

FIG. 12A shows a cross-sectional view of an impeller.

FIG. 12B shows a cross-sectional view of an illustrative embodiment of apump housing.

FIG. 12C shows a cross-sectional view of an illustrative embodiment of amotor and motor housing.

FIG. 13A shows a top perspective view of an illustrative embodiment ofan impeller.

FIG. 13B shows a bottom perspective view of the impeller of FIG. 13A.

FIG. 13C shows a bottom plan view of the impeller of FIG. 13A.

FIG. 14A shows top plan view of an illustrative embodiment of a motorand carrier.

FIG. 14B shows a perspective view of the motor and carrier of FIG. 14A.

FIG. 15A shows a bottom plan view of an illustrative embodiment of animpeller.

FIG. 15B shows a top plan view of an illustrative embodiment of acarrier.

FIG. 16 shows a cross-sectional side view of an illustrative embodimentof a pump.

FIG. 17 shows an enlarged cross-sectional side view of the pump ofsection D of FIG. 16.

In one or more implementations, not all of the depicted components ineach figure may be required, and one or more implementations may includeadditional components not shown in a figure. Variations in thearrangement and type of the components may be made without departingfrom the scope of the subject disclosure. Additional components,different components, or fewer components may be utilized within thescope of the subject disclosure.

DETAILED DESCRIPTION

The detailed description set forth below is intended as a description ofvarious implementations and is not intended to represent the onlyimplementations in which the subject technology may be practiced. Asthose skilled in the art would realize, the described implementationsmay be modified in various different ways, all without departing fromthe scope of the present disclosure. Accordingly, the drawings anddescription are to be regarded as illustrative in nature and notrestrictive.

Referring to the drawings, depicted elements are not necessarily shownto scale, and like or similar elements are designated by the samereference numeral through several views. In some embodiments, thedepicted elements can be provided with the relative size and positionsshown in the several views. Additionally or alternatively, the depictedelements can be provided with relative sizes and positions other thanthose shown in the several views.

Implantable blood pumps can be utilized for total artificial heartreplacement or ventricular assistance. Implantable blood pumps may beutilized for temporary or long term ventricular assistance or topermanently replace a patient's damaged heart. Some blood pumps maymimic the pulsatile flow of the heart. However, some blood pumps haveprogressed to designs that are non-pulsatile. Non-pulsatile blood pumpsare typically rotary and propel fluid with impellers that span thespectrum from radial flow, centrifugal type impellers to axial flow,auger type impellers.

A common issue encountered by blood pumps is blood trauma. The causes ofblood trauma can be partially attributed to shear stress and/or heatgenerated by the bearings supporting the impeller. Shear stress and/orheat may cause hemolysis, thrombosis, and the like. In some blood pumps,the impeller may be driven by a shaft. The shaft may be sealed off withshaft seals to prevent blood from entering undesirable areas, such as amotor driving the shaft. However, shaft seals generate excess heat thatmay produce blood clots, and shaft seals may fail and allow blood toenter unwanted areas.

A great deal of effort has been devoted to reducing or eliminating bloodtrauma in rotary blood pumps. One solution to minimizing or eliminatingblood trauma is to provide hydrodynamic support of the impeller.

For example, hydrodynamic support may be provided by ramp, wedge, plainjournal, multi-lobe or groove hydrodynamic bearings. Another solution isto provide mechanical support of the impeller using mechanical bearings,such as jewel type bearings in the form of a shaft and sleeve or balland cup. These mechanical bearings may utilize biocompatible hardceramic materials. To function properly in blood, a mechanical bearingmust generate very little heat and should avoid stagnant orrecirculating areas of blood flow to prevent the formation of bloodclots. Another solution proposed is the utilization of passive permanentmagnetic and active controlled magnetic bearings to provide impellersupport in blood pumps. Magnetic bearings, hydrodynamic bearings, and/ormechanical bearings may be combined to provide impeller support in bloodpumps.

However, in accordance with at least some of the embodiments disclosedherein is the realization that active magnetic bearing systems mayrequire sensors and complex controls that increase cost and decreasereliability. Hydrodynamic bearings may require small clearances whichmay cause slow moving or stagnant blood flow between hydrodynamicbearing surfaces. Further, some blood pumps incorporate electric motorsinto the pumping chamber, rather than providing separate motor andpumping chambers. For example, a stator may be provided in the pumphousing and magnets can be incorporated into an impeller to provide apump impeller that also functions as the rotor of the electric motor.

Heart pumps that are suitable for adults may call for approximately 5liters/min of blood flow at 100 mm of Hg pressure, which equates toabout 1 watt of hydraulic power. Some implantable continuous flow bloodpumps consume significantly more electric power to produce the desiredamount of flow and pressure.

High power consumption makes it impractical to implant a power source inthe body. For example, size restrictions of implantable power sourcesmay only allow the implantable power source to provide a few hours ofoperation. Instead, high power consumption blood pumps may provide awire connected to the pump that exits the body (i.e., percutaneous) forconnection to a power supply that is significantly larger than animplantable power source. These blood pumps may require external powerto be provided at all times to operate. In order to provide somemobility, external bulky batteries may be utilized. However,percutaneous wires and external batteries can still restrict themobility of a person with such a blood pump implant. For example, suchhigh power consumption blood pumps have batteries that frequentlyrequire recharging thereby limiting the amount of time the person can beaway from a charger or power source, batteries that can be heavy orburdensome thereby restricting mobility, percutaneous wires that canlead to infection and are not suitable for prolonged exposure to watersubmersion (e.g., swimming, bathing, etc.), and/or other additionaldrawbacks.

The various embodiments of blood pumps discussed herein may be suitablefor use as a ventricular assist device (VAD) or the like because theycause minimal blood damage, are energy efficient, and can be powered byimplanted batteries for extended periods of time. Further, these pumpsare also beneficial because they may improve the quality of life of apatient with a VAD by reducing restrictions on the patient's lifestyle.

The various embodiments of blood pumps discussed herein can provideradial, axial, and angular stability to a rotating impeller that isdriven by a separate rotor. Both radial and axial stability can beprovided, at least in part, by one or more permanent magnetic couplingsbetween the rotor and the impeller and/or permanent magnetic bearingsbetween the pump housing and the impeller. For example, adequate radialstability can be provided solely by the magnetic coupling. By furtherexample, axial stability can be provided by balanced forces from themagnetic coupling, a hydrodynamic bearing, and/or fluid pressure andflow about the impeller. Angular stability, defined as the impellerrotating about an axis that is aligned and coaxial with its principlegeometric axis, can be improved by gyroscopic forces created by therotational inertia of the impeller itself. Adequate stability canachieve suspension of the impeller without contacting any portion of thehousing. For example, the impeller can rotate and remain in contact withonly the fluid. Stability can include a balance of opposing forces,where the impeller is balanced by being held in equilibrium between theopposing forces.

The following description provides an implantable, energy efficient,small, and magnetically driven blood pump. FIG. 1 shows a top view of anillustrative embodiment of pump 5. In some embodiments, pump 5 is formedfrom pump housing 30 providing inlet 10, outlet 20, and motor housing100. Pump housing 30 is composed of two or more pieces. FIG. 2 shows across-sectional side view of an illustrative embodiment of pump 5. Insome embodiments, pump housing 30 provides a chamber for impeller 40 torotate within. The impeller chamber has inlet 10 for connection to afluid source and outlet 20 for providing fluid to a desired location.The impeller chamber is sealed and pressure tight to prevent fluid fromentering/exiting the impeller chamber from locations other than inlet 10and outlet 20.

Motor housing 100 is attached to pump housing 30 to form a fluid and/orpressure tight chamber for motor 70. While pump housing 30 is shown as aseparate component from motor housing 100, in other embodiments, pumphousing 30 and motor housing 100 may be combined to form a single,combined housing, for example, formed as a single, continuous part. Anexploded, cross-sectional view of an illustrative embodiment of motor 70and motor housing 100 is also shown in FIGS. 5A-5C.

In accordance with some embodiments, motor housing 100 is shown separatefrom pump housing 30. Motor 70 is entirely contained between pumphousing 30 and motor housing 100. A high-efficiency electric motor canbe utilized, such as an electric motor with efficiency of about 85% orgreater. Motor 70 provides shaft 80 with carrier 60 mounted to shaft 80.Carrier 60 contains one or more permanent magnets and/or magneticmaterials. The motor 70 rotates shaft 80, causing carrier permanentmagnets 55 placed in carrier 60 to rotate. The motor 70 can include astator with one or more coils (not shown) and a rotor with one or morepermanent magnets (not shown) that drive the shaft 80. Accordingly, themotor 70 can directly drive the shaft 80 and carrier 60, rather thandirectly driving the impeller 40.

As shown in FIGS. 4 and 6A-6C, the impeller 40 can comprise one or morearc-shaped segments or blades joined by a disc or ring at the bottom ofimpeller 40. Alternately, the blades may be joined by short and thinribs, struts, or bridges connecting the blades thereby eliminating thebottom disc or ring. One or more of the blades of impeller 40 cancomprise one or more permanent magnets and/or magnetic materials, whichcan be arranged to attract to one or more carrier permanent magnets 55in an axial direction (i.e., along an axis of rotation of the impeller40). Alternately, impeller permanent magnets 50 can reside partially orwholly in the bottom disc or ring joining the impeller blades. Carrierpermanent magnets 55 and impeller permanent magnets 50 may form an axialmagnetic coupling to transmit torque from motor 70 to impeller 40.Rotation of the carrier 60 causes impeller 40 to rotate and move fluidfrom inlet 10 to outlet 20.

As used herein, “magnet” can include a magnet of a hard magneticmaterial and/or a magnet of a soft magnetic material. Hard magneticmaterials include materials that retain their magnetism even after theremoval of an applied magnetic field. Magnets that include hard magneticmaterial can form permanent magnets. Hard magnetic materials includeneodymium (NdFeB), iron-neodymium, iron-boron, cobalt-samarium,iron-chromium-cobalt, and combinations or alloys thereof. Soft magneticmaterials include materials that are responsive to magnetic fields, butdo not retain their magnetism after removal of an applied magneticfield. Magnets that include soft magnetic material can form temporarymagnets. Soft magnetic materials include iron, iron-cobalt,iron-silicon, steel, stainless steel, iron-aluminum-silicon,nickel-iron, ferrites, and combinations or alloys thereof. It will berecognized that “hard magnetic” and “soft magnetic” does not necessarilyrelate to the rigidity of the materials.

In accordance with some embodiments, as shown in FIG. 4, the one or moreimpeller permanent magnets 50 and one or more carrier permanent magnets55 can be arranged to attract in the axial direction (e.g., along anaxis of rotation of the impeller). The impeller permanent magnets 50 andcarrier permanent magnets 55 can create magnetic forces that can act torestrain impeller motion in the radial direction during rotation therebyforming a radial magnetic bearing. As used herein, a magnetic bearing isone that supports an impeller in the indicated direction by tending tomove the impeller to a position of equilibrium. For example, a radialmagnetic bearing can balance the impeller in a radial direction. Themagnets need not be aligned radially to achieve radial stability of theimpeller. Indeed, various magnets disclosed herein form an axialmagnetic coupling to provide radial stability with a radial magneticbearing. By further example, an axial magnetic bearing can balance theimpeller in an axial direction. The magnets need not be aligned axiallyto achieve axial stability of the impeller. Indeed, various magnetsdisclosed herein form a radial magnetic coupling to provide axialstability with an axial magnetic bearing.

The impeller permanent magnets 50 may be sufficiently small in size sothat they have little or no impact on the main fluid flow paths ofimpeller 40 thereby allowing the design of impeller 40 to focus on fullyoptimizing pump efficiency. These benefits can allow pumpingefficiencies of greater than 50% to be achieved.

In some embodiments, no additional mechanism is required to radiallystabilize the impeller 40 during rotation. For example, in someembodiments, only the axially attracting impeller permanent magnets 50and carrier permanent magnets 55 provide radial stability to theimpeller 40. In some embodiments, no magnetic coupling or bearing isrequired radially across or spaced apart from or within the impeller 40.In some embodiments, no support structure is required radially across orspaced apart from or within the impeller 40, for example, to form ahydrodynamic or magnetic bearing.

As used herein, components that are radially across from each other orradially spaced apart from each other are aligned so that they haveoverlapping portions (e.g., as viewed from a side) while being differentradial distances away from an axis. For example, the components can beoverlapping by having positions that are both aligned with a commonportion of the axis.

As used herein, components that are axially across from each other oraxially spaced apart from each other are aligned so that they haveoverlapping portions (e.g., as viewed from above or below) while being asame distance away from an axis. For example, the components can beoverlapping by being arranged along an axis that is parallel to an axisof impeller rotation.

Pump housing 30 provides a bearing surface 120. Impeller 40 may providehydrodynamic bearing features 90 on its bottom surface or surfaces toform an axial hydrodynamic bearing with bearing surface 120.Hydrodynamic bearing features 90 may be ramps, wedges, steps, grooves orany other feature that creates hydrodynamic pressure during rotation.

The impeller 40 is illustrated in FIGS. 6A-6C as a semi-open type (e.g.,having an end plate on one side of impeller). As such, the hydrodynamicbearing features 90 can be provided on or formed by an end plate on oneside of the impeller 40. While the impeller 40 is illustrated as asemi-open type (e.g., having an end plate on one side of impeller), itwill be understood that an impeller can be an open, pressure balancedtype impeller to reduce axial thrust by omitting an end plate on bothsides of the arc-shaped segments. As such, the hydrodynamic bearingfeatures 90 can be formed on the arc-shaped segments even in the absenceof an end plate. Suitable impellers include open type (e.g., no endplates on either side of an impeller), semi-open type (e.g., end plateon one side of an impeller), and closed type (e.g., end plate on bothsides of an impeller). It will be further understood that other types ofimpellers may also be suitable, including other blade shapes androtation in a different direction.

The force created by the axial hydrodynamic bearing acts to separate theimpeller 40 from contacting the pump housing 30 during rotation.Additionally, the force created by the axial hydrodynamic bearing actsopposite to the attractive force created by some of impeller permanentmagnets 50 and carrier permanent magnets 55. By combining the radialmagnetic bearing formed by some of impeller permanent magnets 50 andcarrier permanent magnets 55 with the axial hydrodynamic bearing formedby hydrodynamic bearing features 90 and bearing surface 120, impeller 40is suspended within pump housing 30 with no contact.

The thickness of fluid gap 130 can be determined by the balance betweenthe attractive force created by some of impeller permanent magnets 50and carrier permanent magnets 55 and the opposing hydrodynamic forcecreated by hydrodynamic bearing features 90 and bearing surface 120.Blood component damage is largely affected by shear stress, which inturn is governed by the fluid gap thickness in impeller bearings.Therefore, a large fluid gap is desirable to minimize trauma to bloodcomponents. In order to maximize the thickness of fluid gap 130, theaxial force required to be generated by the hydrodynamic bearing formedbetween hydrodynamic bearing features 90 and bearing surface 120 shouldbe minimized. However, the attractive force generated by some ofimpeller permanent magnets 50 and carrier permanent magnets 55 increasesthe force required from the axial hydrodynamic bearing due to the factthat the attractive magnetic forces must be sufficient to transmitenough torque to impeller 40 during rotation with a reasonable margin ofsafety. Otherwise, impeller 40 may cease to rotate with motor 70 if moretorque is required than can be transmitted by the axial magneticcoupling. This is known as magnetic coupling slippage. Patient safetycan be improved by avoiding magnetic coupling slippage.

In some embodiments, it may be desirable to reduce the force requiredfrom the axial hydrodynamic bearing formed by hydrodynamic bearingfeatures 90 and bearing surface 120. Fluid pressure created by therotation of impeller 40 in the impeller chamber can enter fluid gap 130.This extra pressure assists in axially separating impeller 40 from pumphousing 30 during rotation and decreases the axial force required to begenerated by the axial hydrodynamic bearing. In this manner, impeller 40“self-levitates” using the pressure created by its own rotation. Thiscan allow the thickness of fluid gap 130 to reach relatively largevalues and thereby reduces trauma and damage to blood components passingthrough the axial hydrodynamic bearing.

So that impeller 40 maintains a relatively stable axial position duringoperation, the axial forces generated by (1) impeller permanent magnets50 and carrier permanent magnets 55, (2) hydrodynamic bearing features90 and bearing surface 120, and (3) pressure generated by the rotationof impeller 40 that enters fluid gap 130, should all be balanced.Otherwise, impeller 40 may contact bearing surface 120 or the opposingsurface of pump housing 30 during rotation. The force generated bypressure is equal to the pressure multiplied by the area upon which thepressure acts. Opening 110 on bottom of impeller 40 may be sized toadjust the area upon which pressure generated by the rotation ofimpeller 40 acts. In this way, the force generated by the pressurecreated by the rotation of impeller 40 may be adjusted, so that theaxial forces acting on impeller 40 are balanced. Opening 110 may be ofany size or shape, including circular, triangular, rectangular, square,or the like. Additionally, opening 110 may be comprised of multipleopenings of any shape or size. However, in some embodiments, thecumulative size of opening 110 is not decreased to an extent that causesthe axial force created by pressure caused by rotation of the impellerto exceed the attractive axial force of impeller permanent magnets 50and carrier permanent magnets 55 under any operating condition,otherwise impeller 40 may contact pump housing 30 under such operatingcondition. The opening 110 can be smaller than a closest distancebetween any two radially opposite arc-shaped segments.

It will be recognized that any rotating body possesses angular momentumdue to the product of its rotating inertia and speed. Conservation ofangular momentum can assist in providing stable rotation of a body byresisting forces which would tend to angularly misalign the rotationalaxis from the principle geometric axis. Such misalignment can lead towobble or other undesirable effects. The stabilizing force of a rotatingmass is commonly referred to as a gyroscopic force due to its use ingyroscopes. As an impeller begins to increase rotational speed andlevitate, unbalanced forces acting on the impeller may cause wobble ortilting leading to unstable rotation. If the rotational speed is furtherincreased, thereby increasing angular momentum, gyroscopic force maybegin to counteract the wobble. If rotational speed continues toincrease, any wobble may be effectively reduced to an acceptableamplitude. Conversely, the angular momentum of the impeller may beeffectively increased by increasing rotational inertia withoutincreasing speed. This can be accomplished by removing material frominside the blades and placing a smaller volume of high density material,such as tungsten, near the outer periphery of the blades. In doing so,the rotational inertia can be increased without significantly increasingthe overall weight of the impeller.

In order to increase the torque transmission capability of the axialmagnetic coupling formed between impeller permanent magnets 50 andcarrier permanent magnets 55 without appreciably increasing theattractive axial force between impeller permanent magnets 50 and carrierpermanent magnets 55, carrier permanent magnets 55 contained in carrier60 may be comprised of magnet pairs as shown in FIGS. 7A and 7B. Asshown in FIGS. 7A and 7B, the individual magnets in each pair may bearranged with different magnetic polarities. For example, the carrierpermanent magnets 55 comprise pairs of adjacent magnets that areoriented to have different magnetic polarities. Each pair comprises afirst magnet attractively coupled to a corresponding impeller permanentmagnet 50 and a second magnet repelling the corresponding impellerpermanent magnet 50. The number of pairs of carrier permanent magnets 55can be equal to the number of impeller permanent magnets 50. In thismanner, the impeller permanent magnets 50 within impeller 40 mayexperience both an attractive force and a repelling force both acting inthe same direction tangential to the radius of impeller 40 as carrier 60rotates. This in effect multiplies the force acting to rotate impeller40 and increases the torque capability of the axial magnetic coupling.As the carrier 60 rotates, the carrier permanent magnet 55 attractingthe corresponding impeller permanent magnet 50 can lead in front of thecarrier permanent magnet 55 that repels the corresponding impellerpermanent magnet 50. Accordingly, the carrier permanent magnet 55 thatrepels the corresponding impeller permanent magnet 50 can repulsivelyurge the corresponding impeller permanent magnet 50 from behind. Becausethe second magnets of each magnet pair contained within carrier 60create a repulsive axial force on impeller permanent magnets 50, the netattractive axial force created between impeller permanent magnets 50 andcarrier permanent magnets 55 is largely unchanged compared to singlemagnets located within carrier 60. The opposing force required to begenerated by the axial hydrodynamic bearing formed between hydrodynamicbearing features 90 and bearing surface 120 is also largely unchangedeven with the increased torque capability of the permanent magnetarrangement shown in FIG. 7. Other additional permanent magnets may becontained within carrier 60 to further enhance axial or radial forcesacting on impeller permanent magnets 50 to further increase torquetransmission capability, radial magnetic bearing stiffness, or both.

Referring now to FIGS. 8-15B, some embodiments of the blood pump caninclude magnetic couplings to provide both radial and axial support to arotating impeller. At least some of the features discussed with respectto the embodiments shown in FIGS. 1-7 can be applied to the embodimentsshown in FIGS. 8-15B.

A pump 140 is shown in FIG. 8 and FIG. 9. The pump 140 allows largeclearances between pump housing 170 and impeller 180 to exist duringoperation. Similar or like items can perform the same function as pump 5shown in FIG. 1 and FIG. 2, and the features of such items are not alldiscussed hereafter, for brevity. Impeller radial permanent magnets 200and rotor hub radial permanent magnets 207 can be used to provideadditional torque transmission capability as well as provide additionalaxial restraint of impeller 180. The pump 140 can comprise a motor 220,a rotor 202 comprising a rotor hub 205 and a carrier 210 and, a shaft230. Carrier 210 and/or hub 205 can be separate, joined, integral, orunitary to form rotor 202. Hub 205 contains one or more permanentmagnets and/or magnetic materials. Motor 220 rotates rotor 202 (e.g.,via shaft 230) causing rotor radial permanent magnets 207 placed in hub205 to rotate.

A cross-sectional view of an illustrative embodiment of pump housing 170without impeller 180 is shown in FIGS. 12A-12C. Pump housing 170 mayprovide a non-ferromagnetic and/or non-electrically conductive diaphragm260 separating impeller chamber 265 from the chamber housing the motor.Diaphragm 260 defines cavity 290 providing a region for hub 205 torotate within. Impeller 180 includes one or more permanent magnetsand/or magnetic materials. Impeller radial permanent magnets 200 allowimpeller 180 to be magnetically coupled to hub 205. This radial magneticcoupling allows motor 220 to cause impeller 180 to rotate when motor 220rotates hub 205. Rotor radial permanent magnets 207 in hub 205 andimpeller radial permanent magnets 200 in impeller 180 form a radialmagnetic coupling between the impeller 180 and hub 205. The radialattractive force of the magnetic coupling formed by impeller radialpermanent magnets 200 and rotor radial permanent magnets 207 alsoprovide additional axial restraint of impeller 180. For example, axialmovement of impeller 180 would misalign impeller radial permanentmagnets 200 and rotor radial permanent magnets 207 axially. Theattractive magnetic forces of impeller radial permanent magnets 200 androtor radial permanent magnets 207 would restrain impeller 180 in theaxial direction. Because of the magnetic forces created by impellerradial permanent magnets 200 and rotor radial permanent magnets 207,axial movement of impeller 180 may cause axial force to be exerted onshaft 230 and hub 205 of motor 220, which is then transferred tobearing(s) (not shown) of motor 220.

While impeller radial permanent magnets 200 and rotor radial permanentmagnets 207 are shown as arc-shaped like quadrants of a cylinder in FIG.10, it will be recognized that impeller radial permanent magnets 200 androtor radial permanent magnets 207 may be shaped in a variety ofdifferent manners to provide the radial magnetic coupling. For example,one or more ring-shaped magnets, square/rectangular-shaped magnets,bar-shaped, or the like may be utilized.

Impeller axial permanent magnets 190 and rotor axial permanent magnets195 still provide torque transmission capability as well as radialrestraint of the impeller during rotation. The radial restoring forcesgenerated by impeller axial permanent magnets 190 and rotor axialpermanent magnets 195 may be sufficient to overcome any radial forcescreated by the attraction of impeller radial permanent magnets 200 androtor radial permanent magnets 207. In doing so, no further radialrestraint, such as would be provided by a radial hydrodynamic bearing,may be required. This can allow a large radial bearing gap 270 ofgreater than 0.005″ to exist between impeller 180 and diaphragm 260resulting in minimal shear stress exerted on blood components passingthrough radial bearing gap 270. For example, the radial bearing gap 270can be greater than 0.005″, 0.010″, 0.015″, or 0.020″. Optionally, theradial bearing gap 270 can form a hydrodynamic bearing with ahydrodynamic bearing feature, for example on the diaphragm 260 and/orthe impeller 180; however, such a hydrodynamic bearing is not requiredfor radial stability of the impeller 180, and the radial bearing gap 270can be sufficiently large to avoid hydrodynamic bearing effects therein.

Impeller 180 may provide hydrodynamic bearing features 240 on its bottomsurface or surfaces to form an axial hydrodynamic bearing with bearingsurface 280. Hydrodynamic bearing features 240 may be ramps, wedges,steps, grooves or any other feature that creates hydrodynamic pressureduring rotation.

Hydrodynamic bearing features 240 on the bottom of impeller 180 act tocreate a hydrodynamic bearing and may separate impeller 180 from bearingsurface 280 of pump housing 170 during rotation. However, pressurecaused by the rotation of impeller 180 also acts to lift impeller 180off of bearing surface 280. If these pressure forces become too great,impeller 180 would be pushed to the opposite side of pump housing 170and make contact, potentially leading to hemolysis or other bloodtrauma. Therefore, with respect to the pump 5, described above, theattractive axial forces generated by impeller permanent magnets 50 andcarrier permanent magnets 55 are not to be exceeded by the axial forcesgenerated by hydrodynamic bearing features 90 and the pressure createdby impeller rotation. The size of the fluid gap 130 existing underimpeller 40 during rotation is controlled accordingly.

With respect to the pump 140, the attractive forces of impeller axialpermanent magnets 190 and rotor axial permanent magnets 195 may be madeweaker to allow the pressure created during rotation of impeller 180 tofurther counteract the attractive forces of impeller axial permanentmagnets 190 and rotor axial permanent magnets 195 and allow impeller 180to lift off bearing surface 280 even further during operation, therebyincreasing axial bearing gap 300 and reducing fluid shear stress. Theaxial restraint of the radial coupling formed by impeller radialpermanent magnets 200 and rotor radial permanent magnets 207 would thenbegin restraining the impeller in the axial direction and preventimpeller contact with the opposing side of pump housing 170 and mayresult in a larger axial bearing gap 300 of greater than 0.005″ toreduce fluid shear stress. In this way, the axial magnetic couplingformed between impeller axial permanent magnets 190 and rotor axialpermanent magnets 195 and the radial magnetic coupling formed byimpeller radial permanent magnets 200 and rotor radial permanent magnets207 would both act to restrain impeller 180 in the axial direction andmay allow the axial bearing gap 300 to be larger during rotation thanwould be possible without the radial coupling formed by impeller radialpermanent magnets 200 and rotor radial permanent magnets 207.

By generating relatively weaker attractive axial forces between impelleraxial permanent magnets 190 and rotor axial permanent magnets 195 toallow a larger axial bearing gap 300 during operation, the radialrestoring forces of impeller axial permanent magnets 190 and rotor axialpermanent magnets 195 may be reduced as well, potentially allowingimpeller 180 to contact diaphragm 260 during operation. To help mitigatethis possibility, a magnet arrangement is shown in FIGS. 14A and 14B.One or more of the rotor axial permanent magnets 195 can include twoindividual permanent magnets, such as outer permanent magnet 196 andinner permanent magnet 197. Outer permanent magnet 196 may bering-shaped (e.g., circular, polygonal, or another shape) with innerpermanent magnet 197 residing within outer permanent magnet 196. Bothouter permanent magnet 196 and inner permanent magnet 197 are axiallymagnetized, but are assembled with opposite polarity (i.e., oppositemagnetic field orientation) in the axial direction. The magnetic fieldof outer permanent magnet 196 acts to suppress the magnetic field ofinner permanent magnet 197 because of the opposing polarity (i.e.,opposite magnetic field orientation) and thereby significantly reducesthe axial attractive force with impeller axial permanent magnet 190contained within impeller 180. Reductions in axial force of about 50%have been shown by testing. However, further testing has shown that thismagnet arrangement does not reduce the radial restoring force generatedby impeller axial permanent magnets 190 and rotor axial permanentmagnets 195 near as much with a loss of only about 20% shown duringtesting. This is due to the radial repulsive force generated betweenimpeller axial permanent magnets 190 and outer permanent magnets 196. Asimpeller 180 is radially pushed by fluid pressure forces caused byimpeller rotation, the impeller 180 can be restrained in the radialdirection by radial magnetic forces generated from (1) attractionbetween impeller axial permanent magnets 190 and inner permanent magnets197 and (2) repulsion between impeller axial permanent magnets 190 andouter permanent magnets 196. Therefore, the permanent magnet arrangementshown in FIGS. 14A and 14B can allow a significant increase in the sizeof axial bearing gap 300 while still providing sufficient axial andradial restraint of impeller 180. This alternate embodiment may allowrelatively large radial bearing gap 270 and axial bearing gap 300 ofgreater than 0.005″ to exist during operation and result in reducedblood trauma as compared to bearing gaps created by hydrodynamicbearings alone.

The net attractive force between impeller 180 and carrier 210 can befurther reduced, without decreasing radial restoring forces, byemploying an alternating polarity (i.e., alternating magnetic fieldorientation) arrangement as shown in FIGS. 15A and 15B. In thisconfiguration, impeller axial permanent magnets 190 and inner permanentmagnets 197 are still attracting in the axial direction to maintaintorque transmission capacity, but they now have alternating polaritiesas shown in FIGS. 15A and 15B. Outer permanent magnets 196 alsoalternate polarity (i.e., alternating magnetic field orientation)correspondingly and are arranged to repulse from impeller radialpermanent magnets 200 in both the axial and radial direction. Theserepulsion forces further lower the net attractive force pulling impeller180 down towards bearing surface 280 allowing an even larger axialbearing gap 300 to exist during rotation. The same repulsion forcescreated by outer permanent magnets 196 interacting with impeller radialpermanent magnets 200 can also serve to further increase the radialrestoring forces resisting impeller movement in the radial direction dueto fluid pressure caused by impeller rotation and thereby canbeneficially allow an even larger radial bearing gap 270 to exist duringrotation.

In some embodiments, no additional mechanism is required to radially oraxially stabilize the impeller 180 during rotation. For example, in someembodiments, only the attracting impeller axial permanent magnets 190and rotor axial permanent magnets 195 can provide radial stability andthe attracting impeller radial permanent magnets 200 and rotor radialpermanent magnets 207 along with pressure forces created by impellerrotation can provide axial stability to the impeller 180. In someembodiments, no hydrodynamic bearing is required radially spaced apartfrom or within the impeller 180. In some embodiments, no supportstructure is required radially spaced apart from or within the impeller180, for example, to form a hydrodynamic bearing. In some embodiments,gyroscopic forces may be used to provide angular stability as previouslydescribed.

Referring now to FIGS. 16-17, some embodiments of the blood pump caninclude a magnetic coupling to provide axial support to a rotatingimpeller and a magnetic bearing to provide radial support. At least someof the features discussed with respect to the embodiments shown in FIGS.8-15B can be applied to the embodiments shown in FIGS. 16-17.

A pump 310 is shown in FIG. 16. The pump 310 replaces the axial magneticcoupling of pump 140 with a permanent magnetic bearing formed betweennon-rotating housing axial permanent magnet 320 placed in pump housing330 and impeller axial permanent magnets 340 to provide radial restraintof impeller 350. The housing axial permanent magnet 320 can bering-shaped or formed by a series of similarly polarized magnets thatform a continuous magnetic field. Similar or like items can perform thesame function as pump 140 shown in FIGS. 9-12, and the features of suchitems may not all be discussed hereafter, for brevity. Housing axialpermanent magnet 320 may be a single magnet or include multiple magnetsplaced in a variety of arrangements to produce the required radialrestoring forces while minimizing axial attractive forces. For example,another housing ring magnet may be placed outside or inside housing ringmagnet 320 to enhance radial magnetic bearing stiffness and/or diminishaxial attraction forces. The radial restoring forces generated byhousing axial permanent magnet 320 and impeller axial permanent magnets340 may be sufficient to overcome any radial forces created by theattraction of impeller radial permanent magnets 360 and rotor hub radialpermanent magnets 370 located in rotor hub 375. In doing so, no furtherradial restraint, such as would be provided by a radial hydrodynamicbearing, may be required. This can allow a large radial bearing gap 380of greater than 0.005″ to exist between impeller 350 and diaphragm 390as shown in FIG. 17 resulting in minimal shear stress exerted on bloodcomponents passing through radial bearing gap 380. For example, theradial bearing gap 380 can be greater than 0.005″, 0.010″, 0.015″, or0.020″. Optionally, the radial bearing gap 380 can form a hydrodynamicbearing with a hydrodynamic bearing feature, for example on thediaphragm 390 and/or the impeller 350; however, such a hydrodynamicbearing is not required for radial stability of the impeller 350, andthe radial bearing gap 380 can be sufficiently large to avoidhydrodynamic bearing effects therein.

Impeller 350 may provide hydrodynamic bearing features 400 on its bottomsurface or surfaces to form an axial hydrodynamic bearing with bearingsurface 410 shown in FIG. 17. Hydrodynamic bearing features 400 may beramps, wedges, steps, grooves or any other feature that createshydrodynamic pressure during start-up to oppose the attractive force ofhousing axial permanent magnet 320 and impeller axial permanent magnets340 thereby levitating the impeller. With respect to the pump 310, thepressure created during rotation of impeller 350 may allow impeller 350to lift off bearing surface 410 even further during operation, therebyincreasing axial bearing gap 420 and reducing fluid shear stress. Theaxial restraint of the radial coupling formed by impeller radialpermanent magnets 360 and rotor hub radial permanent magnets 370 wouldthen begin restraining the impeller in the axial direction and preventimpeller contact with the opposing side of pump housing 330 and mayresult in a larger axial bearing gap 420 of greater than 0.005″ toreduce fluid shear stress.

Embodiments disclosed herein include:

-   -   A. A blood pump comprising: a pump housing having an inlet, an        outlet, a first chamber, and a second chamber; a carrier within        the first chamber, the carrier being rotatable by a motor and        comprising carrier permanent magnets; and an impeller within the        second chamber and comprising: impeller permanent magnets that        are axially spaced apart from and magnetically coupled to the        carrier permanent magnets; and    -   B. A method of pumping blood, the method comprising: with a        motor, rotating a carrier within a first chamber of a pump        housing, the carrier comprising carrier permanent magnets; with        the carrier, rotating an impeller within a second chamber of the        pump housing, the impeller comprising impeller permanent magnets        that are axially spaced apart from and forming a magnetic        coupling with the carrier permanent magnets; radially        stabilizing the impeller with the magnetic coupling; and axially        stabilizing the impeller with a hydrodynamic bearing feature on        a side of the impeller facing the carrier.    -   C. A blood pump comprising: a pump housing having an inlet, an        outlet, a first chamber, and a second chamber; a rotor within        the first chamber, the rotor being rotatable by a motor and        comprising: rotor axial permanent magnets; and rotor radial        permanent magnets; and an impeller within the second chamber and        comprising: impeller axial permanent magnets that are axially        spaced apart from and magnetically coupled to the rotor axial        permanent magnets; and impeller radial permanent magnets that        are radially spaced apart from and magnetically coupled to the        rotor radial permanent magnets.    -   D. A method of pumping blood, the method comprising: with a        motor, rotating a rotor within a first chamber of a pump        housing, the rotor comprising rotor axial permanent magnets and        rotor radial permanent magnets; with the rotor, rotating an        impeller within a second chamber of the pump housing, the        impeller comprising impeller axial permanent magnets and        impeller radial permanent magnets; and radially stabilizing the        impeller with an axial magnetic coupling between the impeller        axial permanent magnets and the rotor axial permanent magnets;        and axially stabilizing the impeller with a radial magnetic        coupling between the impeller radial permanent magnets and the        rotor radial permanent magnets.    -   E. A blood pump comprising: a pump housing having an inlet, an        outlet, a first chamber, a second chamber, and a housing axial        permanent magnet; a rotor hub within the first chamber, the        rotor hub being rotatable by a motor and comprising rotor hub        radial permanent magnets; and an impeller within the second        chamber and comprising: impeller axial permanent magnets that        are axially spaced apart from and magnetically attracted to the        housing axial permanent magnet; and impeller radial permanent        magnets that are radially spaced apart from and magnetically        coupled to the rotor hub radial permanent magnets.    -   F. A method of pumping blood, the method comprising: with a        motor, rotating a rotor hub within a first chamber of a pump        housing, the rotor hub comprising rotor radial permanent        magnets; with the rotor hub, rotating an impeller within a        second chamber of the pump housing, the impeller comprising        impeller axial permanent magnets and impeller radial permanent        magnets; radially stabilizing the impeller with a permanent        magnetic bearing formed between the impeller axial permanent        magnets and a housing axial permanent magnet residing within the        pump housing; and axially stabilizing the impeller with a radial        magnetic coupling between the impeller radial permanent magnets        and the rotor radial permanent magnets.

Each of embodiments A, B, C, D, E, and F may have one or more of thefollowing additional elements in any combination:

-   -   Element 1: A hydrodynamic bearing feature on a side of the        impeller facing the carrier.    -   Element 2: The hydrodynamic bearing feature is positioned        between the impeller permanent magnets and the carrier permanent        magnets.    -   Element 3: The impeller is configured to be axially supported        during rotation by a balance of: an axial magnetic coupling        between the impeller permanent magnets and the carrier permanent        magnets; and a hydrodynamic force provided by the hydrodynamic        bearing feature.    -   Element 4: The impeller is configured to be radially supported        during rotation by an axial magnetic coupling between the        impeller permanent magnets and the carrier permanent magnets.    -   Element 5: The impeller is radially stabilized solely with an        axial magnetic coupling.    -   Element 6: The impeller is configured to be radially supported        during rotation by a permanent magnetic bearing formed between        the impeller permanent magnets and the housing axial permanent        magnet.    -   Element 7: The impeller is radially stabilized solely with a        radial magnetic bearing.    -   Element 8: The impeller defines an opening that extends axially        through an entire height of the impeller, wherein no portion of        the pump housing is within the opening.    -   Element 9: The carrier permanent magnets comprise pairs of        adjacent magnets that are oriented to have different magnetic        polarities, wherein each pair comprises a first magnet        attractively coupled to a corresponding impeller permanent        magnet and a second magnet repelling the corresponding impeller        permanent magnet.    -   Element 10: Each of the rotor axial permanent magnets comprises:        an outer permanent magnet; and an inner permanent magnet        extending axially within an interior of the outer permanent        magnet, the inner permanent magnet having a magnetic field        orientation that is opposite a magnetic field orientation of the        outer permanent magnet.    -   Element 11: The rotor radial permanent magnets, the impeller        axial permanent magnets, and the impeller radial permanent        magnets are mutually aligned with a position along an axis of        the blood pump.    -   Element 12: The rotor axial permanent magnets are axially offset        from the rotor radial permanent magnets.

A reference to an element in the singular is not intended to mean oneand only one unless specifically so stated, but rather one or more. Forexample, “a” module may refer to one or more modules. An elementproceeded by “a,” “an,” “the,” or “said” does not, without furtherconstraints, preclude the existence of additional same elements.

Headings and subheadings, if any, are used for convenience only and donot limit the invention. The word exemplary is used to mean serving asan example or illustration. To the extent that the term include, have,or the like is used, such term is intended to be inclusive in a mannersimilar to the term comprise as comprise is interpreted when employed asa transitional word in a claim. Relational terms such as first andsecond and the like may be used to distinguish one entity or action fromanother without necessarily requiring or implying any actual suchrelationship or order between such entities or actions.

Phrases such as an aspect, the aspect, another aspect, some aspects, oneor more aspects, an implementation, the implementation, anotherimplementation, some implementations, one or more implementations, anembodiment, the embodiment, another embodiment, some embodiments, one ormore embodiments, a configuration, the configuration, anotherconfiguration, some configurations, one or more configurations, thesubject technology, the disclosure, the present disclosure, othervariations thereof and alike are for convenience and do not imply that adisclosure relating to such phrase(s) is essential to the subjecttechnology or that such disclosure applies to all configurations of thesubject technology. A disclosure relating to such phrase(s) may apply toall configurations, or one or more configurations. A disclosure relatingto such phrase(s) may provide one or more examples. A phrase such as anaspect or some aspects may refer to one or more aspects and vice versa,and this applies similarly to other foregoing phrases.

A phrase “at least one of” preceding a series of items, with the terms“and” or “or” to separate any of the items, modifies the list as awhole, rather than each member of the list. The phrase “at least one of”does not require selection of at least one item; rather, the phraseallows a meaning that includes at least one of any one of the items,and/or at least one of any combination of the items, and/or at least oneof each of the items. By way of example, each of the phrases “at leastone of A, B, and C” or “at least one of A, B, or C” refers to only A,only B, or only C; any combination of A, B, and C; and/or at least oneof each of A, B, and C.

It is understood that the specific order or hierarchy of steps,operations, or processes disclosed is an illustration of exemplaryapproaches. Unless explicitly stated otherwise, it is understood thatthe specific order or hierarchy of steps, operations, or processes maybe performed in different order. Some of the steps, operations, orprocesses may be performed simultaneously. The accompanying methodclaims, if any, present elements of the various steps, operations orprocesses in a sample order, and are not meant to be limited to thespecific order or hierarchy presented. These may be performed in serial,linearly, in parallel or in different order. It should be understoodthat the described instructions, operations, and systems can generallybe integrated together in a single software/hardware product or packagedinto multiple software/hardware products.

In one aspect, a term coupled or the like may refer to being directlycoupled. In another aspect, a term coupled or the like may refer tobeing indirectly coupled.

Terms such as top, bottom, front, rear, side, horizontal, vertical, andthe like refer to an arbitrary frame of reference, rather than to theordinary gravitational frame of reference. Thus, such a term may extendupwardly, downwardly, diagonally, or horizontally in a gravitationalframe of reference.

The disclosure is provided to enable any person skilled in the art topractice the various aspects described herein. In some instances,well-known structures and components are shown in block diagram form inorder to avoid obscuring the concepts of the subject technology. Thedisclosure provides various examples of the subject technology, and thesubject technology is not limited to these examples. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the principles described herein may be applied to otheraspects.

All structural and functional equivalents to the elements of the variousaspects described throughout the disclosure that are known or later cometo be known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe claims. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the claims. No claim element is to be construedunder the provisions of 35 U.S.C. § 112, sixth paragraph, unless theelement is expressly recited using the phrase “means for” or, in thecase of a method claim, the element is recited using the phrase “stepfor”.

The title, background, brief description of the drawings, abstract, anddrawings are hereby incorporated into the disclosure and are provided asillustrative examples of the disclosure, not as restrictivedescriptions. It is submitted with the understanding that they will notbe used to limit the scope or meaning of the claims. In addition, in thedetailed description, it can be seen that the description providesillustrative examples and the various features are grouped together invarious implementations for the purpose of streamlining the disclosure.The method of disclosure is not to be interpreted as reflecting anintention that the claimed subject matter requires more features thanare expressly recited in each claim. Rather, as the claims reflect,inventive subject matter lies in less than all features of a singledisclosed configuration or operation. The claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparately claimed subject matter.

The claims are not intended to be limited to the aspects describedherein, but are to be accorded the full scope consistent with thelanguage of the claims and to encompass all legal equivalents.Notwithstanding, none of the claims are intended to embrace subjectmatter that fails to satisfy the requirements of the applicable patentlaw, nor should they be interpreted in such a way.

What is claimed is:
 1. A blood pump comprising: a pump housing having aninlet, an outlet, a first chamber, a second chamber, and a housing axialpermanent magnet; a rotor hub within the first chamber, the rotor hubbeing rotatable by a motor and comprising rotor hub radial permanentmagnets; and an impeller within the second chamber and comprising:impeller axial permanent magnets that are axially spaced apart from andmagnetically attracted to the housing axial permanent magnet; andimpeller radial permanent magnets that are radially spaced apart fromand magnetically coupled to the rotor hub radial permanent magnets. 2.The blood pump of claim 1, wherein the impeller is configured to beaxially supported during rotation by a balance of: a permanent magneticbearing between the impeller axial permanent magnets and the housingaxial permanent magnet; a radial magnetic coupling formed between theimpeller radial permanent magnets and the rotor hub radial permanentmagnets; and pressure forces generated by rotation of the impeller. 3.The blood pump of claim 1, wherein the impeller is configured to beradially supported during rotation by a permanent magnetic bearingformed between the impeller axial permanent magnets and the housingaxial permanent magnet.
 4. The blood pump of claim 1, wherein thehousing axial permanent magnet is a ring magnet.
 5. The blood pump ofclaim 4, wherein the pump housing further comprises an additional ringmagnet outside the housing axial permanent magnet.
 6. The blood pump ofclaim 4, wherein the pump housing further comprises an additional ringmagnet inside the housing axial permanent magnet.
 7. The blood pump ofclaim 1, wherein the housing axial permanent magnet is one of a seriesof similarly polarized magnets that form a continuous magnetic field. 8.The blood pump of claim 1, wherein, as the impeller rotates, radialrestoring forces generated by the housing axial permanent magnet and theimpeller axial permanent magnets are sufficient to overcome radialforces created by an attraction of the impeller radial permanent magnetsand the rotor hub radial permanent magnets.
 9. The blood pump of claim1, wherein, radially opposing surfaces of the impeller and the pumphousing do not form a radial hydrodynamic bearing.
 10. The blood pump ofclaim 1, wherein, as the impeller rotates, radially opposing surfaces ofthe impeller and the pump housing are configured to form a radialbearing gap of greater than 0.005″.
 11. The blood pump of claim 1,wherein, as the impeller rotates, radially opposing surfaces of theimpeller and the pump housing are configured to form a radialhydrodynamic bearing.
 12. The blood pump of claim 1, wherein theimpeller further comprises a hydrodynamic bearing feature on a side ofthe impeller facing the housing axial permanent magnet.
 13. The bloodpump of claim 12, wherein the hydrodynamic bearing feature is positionedbetween the impeller axial permanent magnets and the housing axialpermanent magnet.
 14. The blood pump of claim 1, wherein, as theimpeller rotates, axially opposing surfaces of the impeller and the pumphousing are configured to form an axial bearing gap of greater than0.005″.
 15. A method of pumping blood, the method comprising: with amotor, rotating a rotor hub within a first chamber of a pump housing,the rotor hub comprising rotor radial permanent magnets; with the rotorhub, rotating an impeller within a second chamber of the pump housing,the impeller comprising impeller axial permanent magnets and impellerradial permanent magnets; radially stabilizing the impeller with apermanent magnetic bearing formed between the impeller axial permanentmagnets and a housing axial permanent magnet residing within the pumphousing; and axially stabilizing the impeller with a radial magneticcoupling between the impeller radial permanent magnets and the rotorradial permanent magnets.
 16. The method of claim 15, wherein axiallystabilizing the impeller comprises maintaining a balance of: thepermanent magnetic bearing; the radial magnetic coupling; and pressureforces generated by rotation of the impeller.
 17. The method of claim15, wherein, as the impeller rotates, radial restoring forces generatedby the housing axial permanent magnet and the impeller axial permanentmagnets are sufficient to overcome radial forces created by anattraction of the impeller radial permanent magnets and the rotor radialpermanent magnets.
 18. The method of claim 15, wherein, as the impellerrotates, radially opposing surfaces of the impeller and the pump housingdo not form a radial hydrodynamic bearing.
 19. The method of claim 15,wherein, as the impeller rotates, radially opposing surfaces of theimpeller and the pump housing form a radial bearing gap of greater than0.005″.
 20. The method of claim 15, wherein, as the impeller rotates,radially opposing surfaces of the impeller and the pump housing form aradial hydrodynamic bearing.
 21. The method of claim 15, wherein, as theimpeller rotates, axially opposing surfaces of the impeller and the pumphousing form an axial bearing gap of greater than 0.005″.